A boy stands as Sunni Muslims attend Friday prayers at the Al-Taqwa mosque, one of two mosques hit by explosions last Friday, in Lebanon's northern city of Tripoli, August 30, 2013. A Lebanese judge today charged three Lebanese and two Syrians in connection with deadly car bomb blasts against two Sunni mosques last week that left at least 47 people dead and more than 500 wounded.

Syria's two warring sides have directly attacked their opponents in Lebanon with car bombs, roadside bomb ambushes, and rocket attacks, all of which further deepen the bitter Sunni-Shiite rift here and raise fears over the country's stability.

A Lebanese judge today charged three Lebanese and two Syrians in connection with deadly car bomb blasts against two Sunni mosques last week that left at least 47 people dead and more than 500 wounded. The Lebanese suspects include Sheikh Hashem Minkara, the leader of the Islamic Unification Movement-Military Council, a Sunni Islamist organization that is closely allied to Syria. Of the two Syrian suspects, one is reportedly a captain in a branch of Syrian intelligence.

The arrests are further evidence that Syria's 30-month conflict is leaking across the border into Lebanon. Given his history, the alleged involvement of Sheikh Minkara in the mosque bombings in the northern city of Tripoli illustrates the complexities and grim ironies found in the long, tortuous relationship between Syria and Lebanon.

The IUM was founded in Tripoli in 1982 and, despite being a Sunni movement, developed close ties to Shiite Iran and to Hezbollah, the Islamic Republic's Lebanese partner. In the mid-1980s, during Lebanon's 1975-90 civil war, the IUM achieved notoriety for battling Syrian troops in Tripoli.

The IUM was eventually crushed and Sheikh Minkara, who was a military commander of the group, was jailed in Syria without charge. He spent 15 years in Syrian prisons before being released in August 2000. Today, the once hardened anti-Baathist cleric is a close Syria ally and heads the Islamic Unification Movement-Military Council, an offshoot of the IUM.

Also charged Friday was Sheikh Ahmad Gharib, a close associate of Sheikh Minkara, and Mustafa Houri, who had tipped off police that the two sheikhs may have been involved in the mosque bombings. Charges were filed in absentia against two Syrians, Capt. Mohammed Ali Ali, an intelligence officer, and Khodr Lutfi al-Ayrouni.

Mr. Saqr charged Sheikh Gharib and Mr. Houri with tasking the two Syrians to set up a “monitoring and planning cell to carry out terrorist acts in Lebanon, particularly in the north, by preparing bombs and booby-trapping cars and putting them in specific areas, including religious institutions with the aim of killing and assassinating political and religious figures,” according to Beirut's Daily Star newspaper.

The two Syrians were charged with preparing the car bombs and placing them outside the Al-Taqwa and As-Salam mosques where they exploded. The two mosques were popular with Salafist Sunnis and the sheikhs who preached at them were outspoken supporters of the Syrian opposition, which has staged an uprising against the regime of Syrian President Bashar al-Assad. The two preachers were unhurt in the explosions.

If Syrian involvement in the two deadliest attacks since the end of Lebanon's civil war is proven to be true, it will prove embarrassing for the Lebanese government, which includes allies of the Assad regime – and not for the first time.

Confronted with evidence of his culpability that had been provided by a police informant, Mr. Samaha confessed his role and has been in a Lebanese jail for the past 12 months awaiting trial. Also indicted by a Lebanese court for their alleged involvement were Ali Mamlouk, a top Syrian intelligence official, and another Syrian intelligence officer identified as Colonel Adnan.